foamed particles

Abstract

To provide a foamed particle that can yield a polyethylenic resin foamed particle molding having superior in-mold formability and small compression set.SOLUTION: A foamed particle includes linear low-density polyethylene as base resin. The linear low-density polyethylene has a density of 920 kg / m3 or less. The linear low-density polyethylene has a melting point of 120°C or higher and 130°C or lower. The linear low-density polyethylene includes, as copolymerization components, propylene component and at least one α-olefin component (α1) selected from butene component, hexene component and octene component.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to foamed particles.

Background Art

[0002] A polyethylene-based foamed particle molded body formed by in-mold molding of polyethylene-based resin foamed particles is excellent in chemical resistance, cushioning properties, etc., and also excellent in recyclability. For this reason, polyethylene-based resin foamed particle molded bodies are widely used as impact absorbers, heat insulating materials, various packaging materials, etc., as packaging and cushioning materials for electric and electronic parts, packaging and cushioning materials for automotive parts, and various packaging materials from other precision parts to foods. For example, in Patent Document 1, uncrosslinked polyethylene-based resin foamed particles having a specific density, melt flow index, melt tension, and cell diameter, obtained by foaming polyethylene-based resin particles of a specific density, are disclosed for the purpose of being moldable in a wide temperature range and improving surface smoothness.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, since the polyethylene-based foamed particle molded body is used for various applications, a molded body having excellent shape recoverability after compression and a small compression set is required. In such a situation, it is expected that by using linear low-density polyethylene with a low density, a molded body having good compression strength and a reduced compression set can be obtained. However, when linear low-density polyethylene with a low density is used, the in-mold moldability of the obtained foamed particles decreases, and it has been difficult to obtain foamed particles that achieve both a low compression set and good in-mold moldability. An object of the present invention is to provide foamed particles capable of producing a polyethylene-based resin foamed particle molded body having excellent in-mold formability and a small compression set.

Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have found that foamed particles having a linear low density polyethylene having a specific density and melting point and a specific comonomer component as a base resin can solve the above problems. That is, one aspect of the present invention is the foamed particles described in the following [1] to [7]. [1] Foamed particles having a linear low density polyethylene as a base resin, wherein the density of the linear low density polyethylene is 920 kg / m 3 Or less, the melting point of the linear low density polyethylene is 120°C or higher and 130°C or lower, and the linear low density polyethylene contains, as a copolymer component, a propylene component and one or more α-olefin components (α1) selected from a butene component, a hexene component, and an octene component. [2] The foamed particles according to [1] above, wherein the content of the propylene component in the linear low density polyethylene is 0.5 mol% or more and 3 mol% or less. [3] The total of the content of the propylene component and the content of the α-olefin component (α1) in the linear low density polyethylene is 1 mol% or more and 10 mol% or less, and the ratio of the content of the propylene component to the total of the content of the propylene component and the content of the α-olefin component (α1) is 0.1 or more and 0.6 or less. The foamed particles according to [1] or [2] above. [4] The foamed particles according to any one of [1] to [3] above, wherein the biomass degree of the linear low density polyethylene measured by ASTM D 6866 is 40% or more. [5] The foamed particle has a crystalline structure in which, in a DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, a melting peak (intrinsic peak) intrinsic to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) on the high-temperature side of the intrinsic peak, the heat of fusion of the foamed particle is 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less, as described in any one of [1] to [4] above. [6] The foamed particle according to [5] above, wherein the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foamed particle is 0.2 or more and 0.7 or less. [7] The bulk density of the foamed particles is 10 kg / m³ 3 More than 300kg / m 3 The foaming particles described in any one of the above [1] to [6] are as follows: [Effects of the Invention]

[0006] According to the present invention, it is possible to provide foamed particles that can be used to manufacture polyethylene-based resin foamed particle molded articles that have excellent in-moldability and low compression set. [Modes for carrying out the invention]

[0007] [Foaming particles] The foamed particles of the present invention are foamed particles using linear low-density polyethylene as the base resin, wherein the density of the linear low-density polyethylene is 920 kg / m³. 3 The following is the case: the linear low-density polyethylene has a melting point of 120°C or higher and 130°C or lower, and the linear low-density polyethylene is a foamed particle containing, as copolymer components, a propylene component and one or more α-olefin components (α1) selected from butene components, hexene components and octene components.

[0008] (Linear low-density polyethylene) The foamed particles use linear low-density polyethylene as the base resin. In this specification, "using linear low-density polyethylene as the base resin" means that the foamed particles are composed of a resin mainly composed of linear low-density polyethylene. As described later, the foamed particles may also contain polymers other than linear low-density polyethylene, as long as they do not impair the effects of the present invention.

[0009] In this invention, the density is 920 kg / m³. 3 The following is the basis resin, which is linear low-density polyethylene containing a propylene component and one or more α-olefin components (α1) selected from butene, hexene, and octene components as copolymerization components. The hexene component in the linear low-density polyethylene includes 1-hexene and 4-methyl-1-pentene. The octene component in the linear low-density polyethylene includes 1-octene, 2-methylheptene, 3-ethylhexene, etc.

[0010] The linear low-density polyethylene contains, as copolymerization components, a propylene component and one or more α-olefin components (α1) selected from butene, hexene, and octene components. In other words, the linear low-density polyethylene contains a propylene component and one or more α-olefin components (α1) selected from butene, hexene, and octene components as copolymerization components. To put it another way, the linear low-density polyethylene contains a propylene component and an α-olefin component (α1) as copolymerization components, and the α-olefin component (α1) is one or more selected from butene, hexene, and octene components. The linear low-density polyethylene of the present invention can also be described as a copolymer of ethylene, propylene, and one or more α-olefins selected from butene, hexene, and octene, having a linear structure. Typically, linear low-density polyethylene tends to have a lower melting point as its density decreases. When foamed particles are manufactured using such low-density linear low-density polyethylene, the resin undergoes a large change in state when heat is applied, making it prone to excessive softening. This can lead to excessive shrinkage of the foamed particles immediately after foaming, making it difficult to obtain good quality foamed particles. Furthermore, even if foamed particles are obtained, from a similar perspective, the molded product tends to shrink excessively immediately after molding during in-mold molding of the foamed particles, making it difficult to obtain foamed particles with excellent in-moldability. The reason why the moldability in the foamed particles of the present invention is improved is not entirely clear, but it is thought to be as follows. Linear low-density polyethylene containing a propylene component as the copolymer component used in the foamed particles of the present invention has a low density, but a relatively high melting point and tends to undergo gradual changes in physical properties during softening. Therefore, it is thought that by using linear low-density polyethylene containing a propylene component as the copolymer component, foamed particles with excellent moldability can be obtained even with low-density linear low-density polyethylene. Furthermore, in the present invention, by using linear low-density polyethylene that has low density and contains one or more selected from butene, hexene, and octene components as copolymerization components, preferably one or more selected from butene and hexene components, it is possible to obtain resin particles with excellent foaming properties and foamed particles with excellent in-mold moldability.

[0011] From this viewpoint, the content of propylene components (content of components derived from propylene) in linear low-density polyethylene is preferably 0.5 mol% or more and 3 mol% or less. Furthermore, from the viewpoint of making it easier to obtain molded articles with low compression set, the content of components derived from propylene is preferably 0.6 mol% or more, more preferably 0.8 mol% or more, and even more preferably 1 mol% or more. On the other hand, from the viewpoint of improving the in-moldability of foamed particles and making it easier to obtain molded articles with desired mechanical properties, the content of components derived from propylene is more preferably 2 mol% or less. Furthermore, from a similar viewpoint, in linear low-density polyethylene, the ratio of the propylene component content to the total content of the α-olefin component (α1) (content of one or more α-olefin components (α1) selected from butene, hexene, and octene components) is preferably 0.1 or higher, and more preferably 0.2 or higher. On the other hand, the ratio of the propylene component content to the total content of the propylene component and the α-olefin component (α1) is preferably 0.6 or lower, more preferably 0.5 or lower, and even more preferably 0.4 or lower. The above content is the total content when the sum of the components derived from ethylene and the components derived from α-olefins having 3 or more carbon atoms (propylene, butene, hexene, octene, etc.) is taken as 100% by mass. Furthermore, from the viewpoint of making it easier to obtain linear low-density polyethylene having the desired physical properties, the sum of the content of the propylene component and the content of the α-olefin component (α1) in linear low-density polyethylene is preferably 1 mol% or more and 10 mol% or less, and more preferably 3 mol% or more and 8 mol% or less.

[0012] Furthermore, if linear low-density polyethylene includes multiple linear low-density polyethylenes, the range of the propylene component content, the range of the ratio of the propylene component content to the sum of the propylene component content and the α-olefin component (α1) content, and the range of the sum of the propylene component content and the α-olefin component (α1) content in the linear low-density polyethylene represent the range of the propylene component content, the range of the ratio of the propylene component content to the sum of the propylene component content and the α-olefin component (α1) content, and the range of the sum of the propylene component content and the α-olefin component (α1) content in the entire linear low-density polyethylene. The content of each α-olefin-derived component in linear low-density polyethylene is determined by carbon-13 nuclear magnetic resonance (CNC) as explained in the examples. 13 This can be determined by measurement (e.g., 13C-NMR) or other methods.

[0013] Furthermore, the linear low-density polyethylene preferably contains as a main component one or more selected from linear low-density polyethylene A1 containing a propylene component, a butene component, and a hexene component as copolymer components (comonomers), and linear low-density polyethylene A2 containing a propylene component and a butene component as copolymer components (comonomers), and more preferably contains as a main component linear low-density polyethylene A1 containing a propylene component, a butene component, and a hexene component as copolymer components. In this case, the total proportion of linear low-density polyethylene A1 and linear low-density polyethylene A2 in the linear low-density polyethylene is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Also, the total proportion of linear low-density polyethylene A1 and linear low-density polyethylene A2 in the linear low-density polyethylene is 100% by mass or less. Furthermore, from the viewpoint of further improving the in-moldability of the foamed particles, the proportion of linear low-density polyethylene A1 in the linear low-density polyethylene is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. On the other hand, the proportion of linear low-density polyethylene A1 in the linear low-density polyethylene is 100% by mass or less.

[0014] From the viewpoint of being able to stably obtain resin particles with excellent foaming properties and from the viewpoint of being able to stably obtain foamed particles with excellent in-moldability, when linear low-density polyethylene A1 containing a propylene component, a butene component, and a hexene component is used as the linear low-density polyethylene, the content of the butene component (component derived from butene) in the linear low-density polyethylene is preferably 0.5 mol% or more and 6 mol% or less, more preferably 1 mol% or more and 5 mol% or less, and even more preferably 2 mol% or more and 4 mol% or less. Furthermore, the content of the hexene component (component derived from hexene) in the linear low-density polyethylene is preferably 0.2 mol% or more and 5 mol% or less, more preferably 0.5 mol% or more and 4 mol% or less, and even more preferably 0.8 mol% or more and 3 mol% or less. From a similar viewpoint, when linear low-density polyethylene A2 containing a propylene component and a butene component is used as the linear low-density polyethylene, the butene component content in the linear low-density polyethylene A2 is preferably 2 mol% or more and 7 mol% or less, and more preferably 3 mol% or more and 6 mol% or less. The linear low-density polyethylene may also be a mixed resin obtained by mixing multiple linear low-density polyethylenes.

[0015] Furthermore, from the viewpoint of being able to stably improve the foaming properties of resin particles and the two-stage foaming properties of foamed particles, and from the viewpoint of being able to obtain foamed particles that have excellent in-moldability and can stably produce molded articles having desired mechanical properties, when linear low-density polyethylene includes linear low-density polyethylene A1 and / or linear low-density polyethylene A2, the ratio of the content of propylene component (component derived from propylene) to the content of butene component (component derived from butene) in linear low-density polyethylene A1 or linear low-density polyethylene A2 [propylene component content (mol%) / butene component content (mol%)] is preferably 0.1 or more and 1 or less, more preferably 0.2 or more and 0.8 or less, and even more preferably 0.3 or more and 0.6 or less. Furthermore, when the linear low-density polyethylene includes linear low-density polyethylene A1, the ratio of the propylene component (component derived from propylene) to the hexene component (component derived from hexene) in the linear low-density polyethylene A1 [propylene component content (mol%) / hexene component content (mol%)] is preferably 0.5 or more and 2 or less, more preferably 0.6 or more and 1.5 or less, and even more preferably 0.8 or more and 1.4 or less.

[0016] The melt flow rate (MFR) of the linear low-density polyethylene, measured under conditions of a temperature of 190°C and a load of 2.16 kg, is preferably 0.1 g / 10 min or more and 2.0 g / 10 min or less. When the melt flow rate of the linear low-density polyethylene is within this range, the in-moldability of the foamed particles can be further improved. The melt flow rate of the linear low-density polyethylene is more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and even more preferably 0.7 g / 10 min or more. Furthermore, the melt flow rate of the linear low-density polyethylene is more preferably 1.8 g / 10 min or less, even more preferably 1.5 g / 10 min or less, and even more preferably 1.4 g / 10 min or less. The melt flow rate of linear low-density polyethylene is measured under conditions of 190°C and a load of 2.16 kg. More specifically, it can be measured according to the method described in the examples, in accordance with JIS K 7210-1:2014.

[0017] The melting point of the linear low-density polyethylene is 120°C or higher and 130°C or lower. As described above, the linear low-density polyethylene used in the present invention contains, as a copolymerization component, a propylene component and one or more α-olefin components (α1) selected from a butene component, a hexene component, and an octene component. Such linear low-density polyethylene has a low density while having a relatively high melting point tendency. Therefore, it becomes a linear low-density polyethylene having a relatively high melting point that satisfies the above melting point range while having a low density, and it is considered that even a low-density linear low-density polyethylene can obtain excellent in-mold formability foam particles. From such a viewpoint, the melting point of the linear low-density polyethylene is more preferably 122°C or higher, and even more preferably 123°C or higher. On the other hand, from the viewpoint of enhancing the in-mold formability of the foam particles under conditions of low molding pressure, the melting point of the linear low-density polyethylene is preferably 128°C or lower, and more preferably 126°C or lower. The melting point of the linear low-density polyethylene is measured based on JIS K 7121:2012 using the linear low-density polyethylene or resin particles or foam particles as test pieces. Specifically, it can be measured by the method described in the examples.

[0018] The density of the linear low-density polyethylene is 920 kg / m 3 or less. From the viewpoints of easily and efficiently obtaining foam particles with a low bulk density and easily obtaining a foam particle molded body with a small compression set, it is preferably 919 kg / m 3 or less, more preferably 918 kg / m 3 or less, and 917 kg / m 3 or less. On the other hand, the density of the linear low-density polyethylene is preferably 910 kg / m 3 or higher, and from the viewpoint of easily enhancing the in-mold formability of the foam particles, it is more preferably 912 kg / m 3 or higher, and even more preferably 914 kg / m 3 or higher. The density of linear low-density polyethylene is measured, for example, by Method A (water displacement method) described in JIS K7112:1999. When measuring the density of resin from foamed particles, the density of the resin can be measured by using defoamed foamed particles as a measurement sample and performing the above density measurement. Specifically, it can be measured by the method described in the examples.

[0019] From the viewpoint of being able to stably improve the foaming properties of resin particles and the two-stage foaming properties of foamed particles, and from the viewpoint of being able to easily obtain foamed particles that have excellent in-moldability and can stably produce molded products with low compression set, the density ρ (kg / m³) of the linear low-density polyethylene is 3 Preferably, the melting point Tm (°C) of the linear low-density polyethylene satisfies the following formula (1). ρ < 1.14 × Tm + 779 ···(1) Linear low-density polyethylene satisfying formula (1) above tends to have a low density while having a relatively high melting point. Therefore, it can be suitably used as linear low-density polyethylene constituting the foamed particles in the present invention. The difference between the right-hand side (1.14 × Tm + 779) and the left-hand side (density ρ) of equation (1) above, [(1.14 × Tm + 779) - ρ], is more preferably 1 or more, even more preferably 2 or more, even more preferably 3 or more, and even more preferably 4 or more. There is no upper limit, but 10 or less is preferred. By using linear low-density polyethylene that satisfies the above range, foamed particles with excellent in-moldability and molded articles with low compression set can be obtained more stably. In general, linear low-density polyethylene (linear low-density polyethylene that does not contain propylene as a copolymer component) has a density of approximately 910 kg / m³. 3 More than 940kg / m 3The following range is possible, and the melting point can generally be in the range of 110°C to 130°C. However, in general linear low-density polyethylene, the melting point tends to decrease with decreasing density, so it is considered difficult to achieve both low density and high melting point, as in the linear low-density polyethylene of the present invention (linear low-density polyethylene containing propylene as a copolymer component). Therefore, it is considered that general linear low-density polyethylene does not satisfy the relationship in formula (1).

[0020] From the viewpoint of making it easier to obtain foamed particles having the desired physical properties, the heat of fusion of the linear low-density polyethylene is preferably 60 J / g or more, more preferably 70 J / g or more, and even more preferably 75 J / g or more. Also, from the same viewpoint, the heat of fusion of the linear low-density polyethylene is preferably 105 J / g or less, more preferably 100 J / g or less, even more preferably 95 J / g or less, and particularly preferably 90 J / g or less. The heat of fusion of linear low-density polyethylene can be determined from the DSC curve obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K 7122:2012 using linear low-density polyethylene as a test specimen. Specifically, it can be measured by the method described in the examples.

[0021] The linear low-density polyethylene preferably has a biomass content of 40% or more, as measured by ASTM D 6866. Having a biomass content within this range allows for the reduction of fossil resource use in the manufacturing of the molded product and also reduces the amount of carbon dioxide emitted throughout the product's lifecycle. From the above viewpoint, the biomass content of the linear low-density polyethylene as measured by ASTM D 6866 is more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. There is no upper limit, and the biomass content of the linear low-density polyethylene as measured by ASTM D 6866 may be 100% or less, but from the viewpoint of easily improving the in-moldability of the foamed particles, the biomass content of the linear low-density polyethylene as measured by ASTM D 6866 is preferably 95% or less, and more preferably 90% or less. The biomass content is measured by ASTM D 6866 and represents the proportion of naturally derived components contained in the linear low-density polyethylene. Furthermore, the biomass content is measured relative to the linear low-density polyethylene with respect to radioactive carbon 14 This value is determined by measuring the concentration of C.

[0022] <Characteristics and composition of foamed particles> As described above, the foamed particles of the present invention have a specific density and melting point, and the base resin is linear low-density polyethylene containing a propylene component and one or more α-olefin components (α1) selected from butene, hexene, and octene components as copolymer components, and preferably have the following characteristics.

[0023] The foamed particles of the present invention have a bulk density of 10 kg / m³. 3 More than 300kg / m 3 The following foam particles are preferable. The bulk density of the foam particles is preferably 10 kg / m³ from the viewpoint of improving the mechanical properties of the resulting molded article. 3 The above is preferable, and more preferably 13 kg / m 3 The above is preferable, and more preferably 15 kg / m 3 That concludes the explanation. On the other hand, the bulk density of the foamed particles is preferably 300 kg / m³ from the viewpoint of obtaining a molded body with low density. 3 The following, and more preferably 240 kg / m³ 3 The following, and more preferably 200 kg / m 3The following, and more preferably 100 kg / m 3 The following, and more preferably 80 kg / m 3 The following, and more preferably 60 kg / m 3 The following applies: As described below, in the present invention, after pressurizing the obtained foamed particles, a two-stage foaming process is performed by heating them with steam or the like to further foam them, thereby obtaining foamed particles with a higher foaming ratio (lower bulk density). From the viewpoint of obtaining a molded article with low density, two-stage foaming is preferable. When performing two-stage foaming, the bulk density of the foamed particles after the first stage of foaming (before the second stage of foaming) is preferably 60 kg / m³, from the viewpoint of stably obtaining foamed particles having the desired bubble structure. 3 The above is more than 70 kg / m 3 The above is preferable to 80 kg / m 3 That concludes the explanation. On the other hand, when performing two-stage foaming, the bulk density of the foamed particles after the first stage of foaming (before the second stage of foaming) is preferably 240 kg / m³ from the viewpoint of being able to stably obtain foamed particles with low density. 3 The following, preferably 200 kg / m³ 3 The following, and more preferably 180 kg / m³ 3 The following, and more preferably 160 kg / m 3 The following applies: The bulk density can be measured by the method described in the examples.

[0024] The closed-cell ratio of the foamed particles of the present invention is preferably 80% or more. When the closed-cell ratio of the foamed particles is within the above range, the in-moldability of the foamed particles can be further improved. The closed-cell ratio of the foamed particles of the present invention is more preferably 85% or more, even more preferably 88% or more, and even more preferably 90% or more. Furthermore, there is no upper limit to the closed-cell ratio of the foamed particles of the present invention, but it is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The closed-cell ratio can be measured by the method described in the examples.

[0025] The average bubble diameter of the foamed particles of the present invention is preferably 60 μm or more and 200 μm or less. When the average bubble diameter of the foamed particles is within the above range, the in-moldability of the foamed particles can be stably improved. The average bubble diameter of the foamed particles of the present invention is more preferably 70 μm or more, even more preferably 80 μm or more, and even more preferably 100 μm or more. Furthermore, the average bubble diameter of the foamed particles of the present invention is more preferably 180 μm or less, even more preferably 160 μm or less, and even more preferably 140 μm or less. Furthermore, when two-stage foaming is performed, the average bubble diameter of the foamed particles after the first stage of foaming (before the second stage of foaming) is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. Furthermore, when two-stage foaming is performed, the average bubble diameter of the foamed particles after the first stage of foaming (before the second stage of foaming) is preferably 120 μm or less, more preferably 110 μm or less, and even more preferably 100 μm or less. The average bubble diameter can be measured by drawing multiple line segments from the outermost surface of a divided foam particle through its center to the outermost surface of the opposite side in a magnified photograph of the cross-section of the foam particle, and dividing the number of bubbles intersecting each line segment by the total length of the line segments. Specifically, it can be measured by the method described in the examples. The average bubble diameter of the foamed particles can be adjusted to a desired range by controlling the type and amount of foam modifier added to the resin particles, or by adjusting the foaming temperature and the pressure inside the pressure vessel during foaming of the resin particles.

[0026] The foamed particles of the present invention have a crystalline structure in which, in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, a melting peak (intrinsic peak) intrinsic to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear on the high-temperature side of the intrinsic peak, preferably the total heat of fusion of the foamed particles is 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less.

[0027] The aforementioned DSC curve is a DSC curve obtained by differential scanning calorimetry (DSC) in accordance with JIS K7122:2012. Specifically, the DSC curve can be obtained by heating 1 to 3 mg of the foamed particles of the present invention from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter. As described above, it is preferable that the foamed particles of the present invention exhibit, in the DSC curve measured for the foamed particles, a melting peak (intrinsic peak) intrinsic to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) on the high-temperature side of the intrinsic peak.

[0028] I will explain this in more detail next. The aforementioned DSC curve refers to the DSC curve obtained by heating the foamed particles using the measurement method described above (the DSC curve during the first heating). Furthermore, the melting peak (intrinsic peak) specific to linear low-density polyethylene is the melting peak that appears due to the melting of the crystals normally present in the linear low-density polyethylene constituting the foamed particles. On the other hand, the melting peak (high-temperature peak) located at a higher temperature than the intrinsic peak is the melting peak that appears at a higher temperature than the intrinsic peak in the DSC curve during the first heating. When this high-temperature peak appears, it is presumed that secondary crystals are present in the resin. Note that when foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min (second heating), the DSC curve obtained (DSC curve during the second heating) shows only the melting peak due to the melting of crystals normally present in the linear low-density polyethylene constituting the foamed particles. This intrinsic peak appears in both the DSC curve during the first heating and the DSC curve during the second heating, and although the temperature of the peak peak may differ slightly between the first and second heatings, the difference is usually less than 5°C. This allows for confirmation of which peak is the intrinsic peak. Furthermore, the foamed particles of the present invention are foamed particles in which, when heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C at a heating rate of 10°C / min, only the melting peak (intrinsic peak) characteristic of linear low-density polyethylene appears in the DSC curve obtained during the second heating.

[0029] The total heat of fusion of the foamed particles of the present invention is the sum of the heats of fusion of all melting peaks (endothermic peaks) appearing in the DSC curve. Preferably, the total heat of fusion of the foamed particles of the present invention is 70 J / g or more and 100 J / g or less. When the total heat of fusion of the foamed particles is within the above range, it is possible to stably obtain foamed particles with excellent two-stage foaming properties and in-mold moldability, and it is also easier to obtain molded articles with excellent strength. From the viewpoint of improving the strength of the resulting molded article, the total heat of fusion of the foamed particles of the present invention is more preferably 72 J / g or more, even more preferably 75 J / g or more, and even more preferably 78 J / g or more. Furthermore, from the viewpoint of improving the two-stage foaming properties and in-moldability of the foamed particles, the total heat of fusion of the foamed particles of the present invention is more preferably 95 J / g or less, even more preferably 90 J / g or less, and even more preferably 85 J / g or less. The total heat of fusion of foamed particles can be determined from the DSC curve obtained by performing differential scanning calorimetry (DSC) on the foamed particles as a test specimen in accordance with JIS K 7122:2012. Specifically, first, for conditioning the test specimen, "(2) When measuring the melting temperature after performing a certain heat treatment" is adopted, and the test specimen is heated from 23°C to 200°C at a heating rate of 10°C / min, and after reaching 200°C, it is cooled from 200°C to 23°C at a rate of 10°C / min, and then heated again from 23°C to 200°C at a rate of 10°C / min to obtain the DSC curve (DSC curve for the second heating). The point at a temperature of 80°C on the obtained DSC curve for the second heating is denoted as α, and the point on the DSC curve corresponding to the melting end temperature is denoted as β. By measuring the area of ​​the region enclosed by the DSC curve in the interval between points α and β and the line segment (α-β), the heat of fusion of the foamed particles can be calculated from this area.

[0030] The heat of fusion of the high-temperature peak of the foamed particles of the present invention is preferably 10 J / g or more and 50 J / g or less. When the heat of fusion of the high-temperature peak of the foamed particles is within this range, even if the foamed particles have a low bulk density, the in-moldability of the foamed particles can be improved, and foamed particles with a wide range of molding pressures over which in-molding is possible can be obtained. As a result, good molded articles can be obtained over a wide density range. The heat of fusion at the high temperature peak of the foamed particles of the present invention is more preferably 15 J / g or more, even more preferably 20 J / g or more, even more preferably 30 J / g or more, even more preferably 32 J / g or more, and especially preferably 34 J / g or more, from the viewpoint of suppressing shrinkage of the molded article immediately after molding and improving the in-moldability of the foamed particles, even when the foamed particles have a lower bulk density, and from the viewpoint of stably suppressing the shrinkage of the second-stage foamed particles when the foamed particles are foamed in two stages. Furthermore, the heat of fusion at the high temperature peak of the foamed particles of the present invention is more preferably 50 J / g or less, more preferably 45 J / g or less, and even more preferably 42 J / g or less, from the viewpoint of improving the fusion properties of the foamed particles under low molding pressure conditions and improving the in-moldability of the foamed particles, and from the viewpoint of making it easier to obtain foamed particles with a lower bulk density when the foamed particles are foamed in two stages. The heat of fusion at the high-temperature peak can be determined using foamed particles as test specimens by differential scanning calorimetry in accordance with JIS K7122:2012. Specifically, it can be determined from the DSC curve (DSC curve for the first heating) obtained by heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / min, and more specifically, it can be measured by the method described in the examples.

[0031] The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foamed particles of the present invention [heat of fusion of high-temperature peak / total heat of fusion] is preferably 0.2 or more and 0.7 or less. When the aforementioned heats of fusion are within the above range, and the ratio is within the above range, foamed particles with excellent in-moldability and a wide molding pressure range that allows in-mold molding over a wide density range can be obtained. Furthermore, foamed particles with good two-stage foaming properties can be obtained. The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foamed particles of the present invention is more preferably 0.3 or higher, even more preferably 0.35 or higher, and even more preferably 0.40 or higher, from the viewpoint of suppressing shrinkage of the molded article immediately after molding and improving the in-moldability of the foamed particles, even when the foamed particles have a lower bulk density, and from the viewpoint of stably suppressing the shrinkage of the two-stage foamed particles when the foamed particles are foamed in two stages. Furthermore, the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foamed particles of the present invention is more preferably 0.6 or lower, even more preferably 0.55 or lower, and even more preferably 0.52 or lower, from the viewpoint of improving the fusion properties of the foamed particles under low molding pressure conditions and improving the in-moldability of the foamed particles, and from the viewpoint of making it easier to obtain foamed particles with a lower bulk density when the foamed particles are foamed in two stages. The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion can be calculated from the total heat of fusion and the heat of fusion of the high-temperature peak.

[0032] The biomass content of the foamed particles of the present invention, as measured by ASTM D 6866, is preferably 40% or more. Having a biomass content within this range allows for the reduction of fossil resource use during the manufacturing of the molded product and also reduces the amount of carbon dioxide emitted throughout the product's lifecycle. From the above viewpoint, the biomass content of the foamed particles of the present invention, as measured by ASTM D 6866, is more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. There is no upper limit, and the biomass content of the foamed particles of the present invention, as measured by ASTM D 6866, may be 100% or less. However, from the viewpoint of improving the in-moldability of the foamed particles, the biomass content of the foamed particles of the present invention, as measured by ASTM D 6866, is more preferably 95% or less, and even more preferably 90% or less. The biomass content is measured by ASTM D 6866 and represents the proportion of naturally derived components contained in the foamed particles of the present invention. Furthermore, the biomass content is measured relative to the foamed particles by radioactive carbon 14 It can be calculated by measuring the concentration of C, or by comparing the biomass content of the biomass-derived resin used to manufacture the foamed particles with the proportion of the biomass-derived resin in the foamed particles.

[0033] The melt flow rate (MFR) of the foamed particles, measured under conditions of a temperature of 190°C and a load of 2.16 kg, is preferably between 0.1 g / 10 min and 2.0 g / 10 min. When the melt flow rate of the foamed particles is within this range, the in-moldability of the foamed particles can be further improved. The melt flow rate of the foamed particles is more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and even more preferably 0.7 g / 10 min or more. Furthermore, the melt flow rate of the foamed particles is more preferably 1.8 g / 10 min or less, even more preferably 1.5 g / 10 min or less, and even more preferably 1.4 g / 10 min or less. The melt flow rate of foamed particles is a value measured under conditions of 190°C and a load of 2.16 kg. More specifically, it can be measured according to the method described in the examples, in accordance with JIS K 7210-1:2014. In addition, foamed particles that have undergone defoaming treatment may be used as the measurement sample to measure the melt flow rate.

[0034] Furthermore, it is preferable that the foamed particles are not crosslinked. Being non-crosslinked makes it easier to recycle the foamed particles, thus reducing the environmental impact. In this specification, "non-crosslinked" means that the proportion of insoluble matter in the foamed particles obtained by the thermal xylene extraction method is 5% by mass or less. From the viewpoint of facilitating the recycling of foamed particles, the proportion of insoluble matter obtained by the thermal xylene extraction method of the foamed particles is preferably 3% by mass or less, and most preferably 0%. The xylene-insoluble content of foamed particles obtained by the thermal xylene extraction method can be measured as follows: First, approximately 1 g of accurately weighed foamed particles (let's call its exact mass M (g)) is placed in a 150 mL round-bottom flask, 100 mL of xylene is added, and the mixture is heated on a mantle heater and refluxed for 6 hours. Then, the remaining residue (insoluble content) is filtered through a 100-mesh wire mesh and dried in a vacuum dryer at 80°C for at least 8 hours. The mass m (g) of the dried material obtained by drying the residue is measured, and the ratio of m to M is expressed as a percentage to determine the proportion of xylene-insoluble content in the foamed particles.

[0035] The average mass per foam particle of the present invention (the arithmetic mean of the masses of 100 randomly selected particles) is preferably 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and even more preferably 0.4 to 2 mg. The average mass per foam particle can be calculated by measuring the mass of 100 randomly selected foam particles and taking the arithmetic mean of these masses.

[0036] Furthermore, the foamed particles of the present invention may contain additives as appropriate, within a range that does not impair the effects of the present invention. Examples of additives include antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, and foam regulators. These additives can be incorporated into the foamed particles, for example, by adding them during the resin particle manufacturing process.

[0037] As a foam regulator, for example, inorganic powders or organic powders can be used. Examples of inorganic powders include metal borate salts such as zinc borate and magnesium borate, and examples of organic powders include fluororesin powders such as polytetrafluoroethylene (PTFE). From the viewpoint of stably obtaining foamed particles that have the desired bulk density and have little variation in bubble diameter, the amount of bubble regulator blended in the resin particles is preferably 50 ppm by mass or more and 5000 ppm by mass or less, more preferably 100 ppm by mass or more and 2000 ppm by mass or less, and even more preferably 150 ppm by mass or more and 1500 ppm by mass or less. Furthermore, from the viewpoint of easily adjusting the average bubble diameter of the foamed particles to a desired range, it is preferable to use a metal borate salt as a bubble regulator, and more preferably zinc borate. When zinc borate is used, the arithmetic mean particle diameter based on the number of particles is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 8 μm or less. The arithmetic mean particle diameter of zinc borate, based on the number of particles, can be determined by first obtaining a particle size distribution based on the number of particles, which is obtained by converting the volume-based particle size distribution measured by laser diffraction scattering by assuming the particle shape to be spherical, and then taking the arithmetic mean of the particle diameters based on this number-based particle size distribution. Note that the above particle diameter refers to the diameter of a hypothetical sphere having the same volume as the particles.

[0038] The foamed particles of the present invention may contain polymers other than linear low-density polyethylene, such as resins or elastomers, to the extent that they can achieve the objectives of the present invention and do not impede the effects of the present invention. Resins other than linear low-density polyethylene include, for example, linear low-density polyethylene that does not contain propylene as a copolymer component, and linear low-density polyethylene that contains components derived from α-olefins other than butene, hexene, and octene. In this case, the content of polymers other than linear low-density polyethylene in the foamed particles is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of linear low-density polyethylene. The content of polymers other than linear low-density polyethylene in the foamed particles may be 0 parts by mass or not at all.

[0039] The foamed particles of the present invention may have a fusion layer on their surface to enhance the fusion properties between the foamed particles during in-mold molding. The fusion layer may be present on the entire surface of the foamed particles or on only a part of the surface. Examples of resins constituting the fusion layer include crystalline polyolefin resins having a melting point lower than the melting point of the linear low-density polyethylene constituting the foamed particles, and amorphous polyolefin resins having a softening point lower than the melting point of the linear low-density polyethylene constituting the foamed particles. The method for forming a fusion layer on the surface of foamed particles is not particularly limited. Examples include a method of foaming resin particles having a fusion layer on their surface, or a method of obtaining foamed particles and then attaching a fusion layer to the surface of the foamed particles. When obtaining foamed particles by foaming resin particles having a fusion layer on their surface, it is preferable to employ a method in which, when manufacturing the resin particles, a fusion layer is laminated onto the surface of the resin particles by co-extruding a molten resin for forming the resin particle body and a molten resin for forming the fusion layer using an extruder capable of co-extrusion.

[0040] As described above, the foamed particles of the present invention can be suitably used as foamed particles for in-mold molding. Furthermore, when the relationship of specific heat of fusion is satisfied, the foamed particles of the present invention become foamed particles with excellent foaming properties during two-stage foaming, and are therefore also suitable as foamed particles for two-stage foaming. On the other hand, when the foamed particles of the present invention satisfy a specific relationship of heat of fusion, they become foamed particles with appropriate flexibility and resilience. Therefore, in this case, the foamed particles of the present invention can be suitably used, for example, as filling beads for cushioning materials. Filling beads are particulate fillings used to fill a bag to form a cushioning material, and the foamed particles of the present invention can be suitably used in particular as filling beads for bead cushions.

[0041] <Method for manufacturing foamed particles> As described above, the foamed particles of the present invention use linear low-density polyethylene as the base resin, and the density of the linear low-density polyethylene is 920 kg / m³. 3 The following conditions apply: the linear low-density polyethylene has a melting point of 120°C or higher and 130°C or lower; and the linear low-density polyethylene is a foamed particle containing, as a copolymer component, a propylene component and one or more α-olefin components (α1) selected from butene, hexene, and octene components. There are no particular restrictions on the method of manufacturing the foamed particle. The foamed particle can be manufactured, for example, by impregnating resin particles using the linear low-density polyethylene as a base resin with a foaming agent, and foaming the resin particles containing the foaming agent. The resin particles using the linear low-density polyethylene as a base resin have a density of 920 kg / m³. 3 The following conditions apply, and it is preferable that the linear low-density polyethylene has a melting point of 120°C or higher and 130°C or lower, and that the linear low-density polyethylene is a resin particle containing, as a copolymer component, a propylene component and one or more α-olefin components (α1) selected from butene components, hexene components and octene components. An example of a suitable manufacturing method is shown below.

[0042] A preferred method for producing foamed particles of the present invention is a method for producing foamed particles by foaming resin particles using linear low-density polyethylene as a base resin, wherein the resin particles containing a foaming agent, dispersed in an aqueous medium in a container, are released from the container together with the aqueous medium into a pressure atmosphere lower than the pressure inside the container, thereby foaming the resin particles. More specifically, the process includes a dispersion step of dispersing the resin particles in an aqueous medium inside a container, a foaming agent impregnation step of impregnating the resin particles with a foaming agent inside the container, and a foaming step of releasing the resin particles containing the foaming agent together with the aqueous medium from the container into a pressure atmosphere lower than the pressure inside the container to foam the resin particles.

[0043] (Manufacturing of resin particles using linear low-density polyethylene as the base resin) The resin particles used in the production of foamed particles of the present invention can be obtained by supplying linear low-density polyethylene, a foam adjusting agent as needed, etc. into an extruder, heating and kneading to form a resin molten product, and then extruding the resin molten product from the extruder while pelletizing it using a strand cut method, a hot cut method, an underwater cut method, etc.

[0044] The average mass per resin particle is preferably adjusted to 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and even more preferably 0.4 to 2 mg. The external shape of the particles is not particularly limited as long as it can achieve the intended purpose of the present invention, but is preferably cylindrical. When the external shape of the resin particles is cylindrical, the particle diameter (length in the extrusion direction) of the resin particles is preferably 0.1 to 3.0 mm, and more preferably 0.3 to 1.5 mm. Furthermore, the ratio (length / diameter) of the length of the resin particles in the extrusion direction to the length in the direction perpendicular to the extrusion direction (diameter of the resin particles) is preferably 0.5 to 5.0, and more preferably 1.0 to 3.0.

[0045] When pelletizing using the strand-cutting method, the particle size, length / diameter, and average mass of the resin particles can be adjusted by appropriately changing the extrusion speed when extruding the molten resin, the strand take-up speed, and the cutter speed when cutting the strands during pelletizing.

[0046] (Manufacturing of foamed particles) A preferred method for producing foamed particles of the present invention includes a dispersion step of dispersing the resin particles in an aqueous medium in a container, a foaming agent impregnation step of impregnating the resin particles with a foaming agent in the container, and a foaming step of releasing the resin particles containing the foaming agent together with the aqueous medium from the container into a pressure atmosphere lower than the pressure inside the container to foam the resin particles. It is preferable that these steps be performed in this order, and more preferably that these steps be performed as a series of steps. This series of steps for foaming is also called a dispersion medium release foaming method.

[0047] In the dispersion step described above, an aqueous dispersion medium is preferably used as the dispersion medium for dispersing the resin particles obtained as described above in a sealed container. The aqueous dispersion medium is a dispersion medium mainly composed of water. The proportion of water in the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. Examples of dispersion media other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, ethanol, etc.

[0048] In the dispersion medium foaming method suitably used in the present invention, it is preferable to add a dispersant to the dispersion medium so that the heated resin particles in the container do not fuse together within the container. Any dispersant that prevents the fusion of resin particles within the container is acceptable, but inorganic dispersants are preferably used. Examples of inorganic dispersants include natural or synthetic clay minerals such as amsnite, kaolin, mica, and clay, as well as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide. One of these may be used, or two or more may be used in combination. Among these, natural or synthetic clay minerals are preferred. The amount of dispersant added is preferably 0.001 to 5 parts by mass per 100 parts by mass of the resin particles.

[0049] Furthermore, when using a dispersant, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, or sodium oleate as a dispersing aid. It is preferable to add the dispersing aid in an amount of about 0.001 to 1 part by mass per 100 parts by mass of the resin particles.

[0050] In the foaming agent impregnation step, it is preferable to use a physical foaming agent for foaming the resin particles. Examples of physical foaming agents include inorganic physical foaming agents and organic physical foaming agents. Examples of inorganic physical foaming agents include carbon dioxide, air, nitrogen, helium, argon, etc. Examples of organic physical foaming agents include aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane; cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; halogenated hydrocarbons such as ethyl chloride, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene. The physical foaming agents may be used alone or in combination of two or more. In addition, inorganic and organic physical foaming agents may be used in combination. From the viewpoint of facilitating the production of desired foamed particles, the foaming agent used in this manufacturing method is preferably an inorganic physical foaming agent, and more preferably carbon dioxide.

[0051] The amount of foaming agent to be added is determined by considering the desired bulk density of the foamed particles and the type of foaming agent, but for example, when using a physical foaming agent, the amount of physical foaming agent added per 100 parts by mass of resin particles is preferably 0.1 to 30 parts by mass, and more preferably 0.5 to 15 parts by mass.

[0052] In the foam particle manufacturing process, a preferred method for impregnating resin particles with a foaming agent is to disperse the resin particles in an aqueous dispersion medium in a sealed container, inject the foaming agent into the sealed container under pressure, and then heat and pressurize the sealed container and maintain that pressure to impregnate the resin particles with the foaming agent.

[0053] In the foaming process, the pressure inside the sealed container during foaming (internal pressure) is preferably 0.5 MPa(G) or higher, more preferably 0.8 MPa(G) or higher. The upper limit is preferably 4 MPa(G) or lower, more preferably 3 MPa(G) or lower. Within this range, the desired foamed particles can be safely produced without the risk of damage or explosion of the sealed container. Furthermore, it is preferable to raise the temperature to 100 to 200°C, more preferably 130 to 160°C, hold it at that temperature for about 5 to 30 minutes, and then release the resin particles containing the foaming agent from the sealed container into an atmosphere with a pressure lower than the pressure inside the sealed container (for example, under atmospheric pressure) to cause foaming.

[0054] Furthermore, the foamed particles of the present invention having a crystal structure in which an intrinsic peak and a high-temperature peak appear in the first DSC curve can be manufactured, for example, as follows. First, resin particles dispersed in a dispersion medium in a sealed container are heated from (melting point of linear low-density polyethylene constituting the resin particles -15°C) to (melting point of linear low-density polyethylene constituting the resin particles +10°C), and held at this temperature for a sufficient time, preferably 10 to 60 minutes (holding step). Next, foamed resin particles that have undergone this holding step can be obtained to produce foamed particles exhibiting the melting peak described above. In the production of foamed particles, resin particles that have undergone the holding step may be prepared in advance, and foamed may be obtained by foaming these resin particles that have undergone the holding step. Alternatively, for example, the holding step may be performed on the resin particles as part of the dispersion step or the foaming agent impregnation step, and foamed may be obtained by foaming the resin particles that have undergone this holding step. From the viewpoint of increasing the productivity of foamed particles, it is preferable to perform the above holding step by heating resin particles dispersed in a dispersion medium in a sealed container in the presence of a foaming agent, and then releasing the contents of the sealed container into an atmosphere with a pressure lower than the pressure inside the sealed container, thereby foaming the resin particles and obtaining foamed particles exhibiting the melting peak described above.

[0055] Furthermore, by foaming the foamed particles obtained as described above in multiple stages, foamed particles with a higher foaming ratio (lower bulk density) can be obtained. For example, by pressurizing the foamed particles with air or the like to increase the pressure inside the bubbles (internal pressure), and then heating them with steam or the like to further foam them (two-stage foaming), foamed particles with an even higher foaming ratio (lower bulk density) can be obtained. From the viewpoint of obtaining a molded body with low density, two-stage foaming is preferable.

[0056] [Foam particle molded body] The foamed particle molded article of the present invention is obtained by molding the foamed particles in a mold. Specifically, linear low-density polyethylene is used as the base resin, and the density of the linear low-density polyethylene is 920 kg / m³. 3 The linear low-density polyethylene has a melting point of 120°C or higher and 130°C or lower, and the linear low-density polyethylene is formed by in-mold molding foamed particles containing a propylene component and one or more α-olefin components (α1) selected from butene, hexene, and octene components as copolymer components.

[0057] The foamed particle molded article of the present invention can be manufactured by filling a mold with foamed particles and then heat-molding it using a heating medium such as steam. Specifically, after filling a mold with foamed particles, a heating medium such as steam is introduced into the mold to heat and expand (secondary foaming) the foamed particles, causing them to fuse together and form the shape of the molded space. Alternatively, in-mold molding in the present invention can also be performed by a pressure molding method (for example, Japanese Patent Publication No. 51-22951) in which the foamed particles are pre-pressurized with a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles, the pressure inside the foamed particles is adjusted to a pressure 0.01 to 0.3 MPa higher than atmospheric pressure, the foamed particles are filled into a mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied into the mold to heat and fuse the foamed particles. Furthermore, the product can also be molded using a compression filling molding method (Japanese Patent Publication No. 4-46217), in which foam particles pressurized to a pressure exceeding atmospheric pressure are filled into a mold pressurized to a pressure exceeding atmospheric pressure using compressed gas, and then a heating medium such as steam is supplied into the cavity to heat and fuse the foam particles. In addition, the product can also be molded using an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795), in which foam particles with high secondary foaming strength obtained under special conditions are filled into the cavity of a mold under atmospheric pressure or reduced pressure, and then a heating medium such as steam is supplied to heat and fuse the foam particles, or a method combining the above methods (Japanese Patent Publication No. 6-22919).

[0058] From the viewpoint of improving mechanical properties, the density of the foamed particle molded article of the present invention is preferably 10 kg / m³. 3 The above is preferable, and more preferably 13 kg / m 3 The above is preferable, and more preferably 15 kg / m 3 That concludes the explanation. Furthermore, from the viewpoint of obtaining a lightweight molded body, the density of the foamed particle molded body is preferably 240 kg / m³. 3 The following, and more preferably 200 kg / m³ 3 The following, and more preferably 100 kg / m 3 The following, and more preferably 80 kg / m 3 The following, and particularly preferably 60 kg / m 3The following applies: The density of the foamed particle molded body is calculated by dividing the mass of the foamed particle molded body by the volume calculated based on the dimensions of the foamed particle molded body, and can be measured by the method described in the examples.

[0059] The foamed particle molded body of the present invention is lightweight and has excellent mechanical properties, and can therefore be used as a shock absorber, heat insulating material, and various packaging materials for applications such as food transport containers, packaging and cushioning materials for electrical and electronic components, vehicle components such as automobile bumpers, building components such as housing insulation materials, and general merchandise. [Examples]

[0060] Next, the present invention will be described in more detail with reference to examples, but these examples do not limit the present invention in any way.

[0061] [Measurement and Evaluation] The following measurements and evaluations were performed on the resins, foamed particles, and molded foamed particle articles used in the examples and comparative examples. The evaluation of the foamed particles or molded foamed particle articles was carried out after conditioning them for two days under conditions of 50% relative humidity, 23°C, and 1 atm.

[0062] <Effervescence Evaluation (Fermentation temperature range for obtaining good quality products)> In the foaming of resin particles described later in the <Production of Foamed Particles> section, foamed particles (single-stage foamed particles) were produced by changing the foaming temperature in increments of 0.1°C. During this process, the equilibrium vapor pressure in the sealed container was set to 4.0 MPa(G). The bulk density and state of the foamed particles obtained by foaming at each foaming temperature were evaluated. Specifically, the bulk density was 100 kg / m³. 3 The foaming temperature at which good products can be obtained was defined as the temperature at which good products can be obtained, provided that the foamed particles do not have any clear wrinkles and almost no shrinkage of the foamed particles is observed. Based on this, the foaming temperature range at which good products can be obtained was evaluated. The wider the range from the lower limit to the upper limit of the foaming temperature range for obtaining good quality products, the better the foaming properties of the resin particles during foaming, and therefore the more suitable the material is.

[0063] <Biomass content of linear low-density polyethylene, biomass content of foamed polyethylene particles> The biomass content of the linear low-density polyethylene used in the examples and comparative examples was determined in accordance with ASTM D 6866, based on radiocarbon 14 This value was determined by measuring the concentration of C. Furthermore, the biomass content of the foamed particles was calculated from the biomass content of the biomass-derived resin used to manufacture the foamed particles and the proportion of the biomass-derived resin contained in the foamed particles.

[0064] <Density of linear low-density polyethylene> The density (ρ) of the linear low-density polyethylene used in the examples and comparative examples was measured according to Method A (water displacement method) of JIS K 7112:1999.

[0065] <Content of α-olefin-derived components in linear low-density polyethylene> The content of each α-olefin-derived component in linear low-density polyethylene is determined by the following carbon-13 nuclear magnetic resonance (CNC) 13 This was determined by 13C-NMR. First, linear low-density polyethylene was dissolved in a mixed solvent of o-dichlorobenzene-d4(ODCB):benzene-d6(C6D6)=4:1 (130°C) to prepare a 10 wt / vol% measurement solution. A JEOL ECZ-400S nuclear magnetic resonance spectrometer was used. 13 NMR of the measurement solution with C as the measurement nucleus ( 13 ¹

[0066] <Melt Flow Rate (MFR) of Linear Low-Density Polyethylene and Foamed Particles> The melt flow rate (MFR) of linear low-density polyethylene used in the examples and comparative examples, as well as the melt flow rate (MFR) of the foamed particles used in the examples and comparative examples, were measured in accordance with JIS K7210-1:2014 under conditions of 190°C and a load of 2.16 kg. For the measurement of the melt flow rate of the foamed particles, the foamed particles were first degassed by hot-pressing them for 3 minutes on a heated press plate heated to 160°C, thereby producing a resin sheet made of the resin constituting the foamed particles. The melt flow rate was then measured using pellet-shaped samples obtained by cutting this resin sheet.

[0067] <Melting point of linear low-density polyethylene> The melting point (Tm) of the linear low-density polyethylene used in the examples and comparative examples was measured by differential scanning calorimetry based on JIS K7121:2012. A high-sensitivity differential scanning calorimetry instrument, "EXSTAR DSC7020" (manufactured by SII Nanotechnology Co., Ltd.), was used. For conditioning the test specimens, "(2) When measuring the melting temperature after performing a certain heat treatment" was adopted. The test specimens were heated from 23°C to 200°C at a heating rate of 10°C / min under a nitrogen inflow of 30 mL / min, then maintained at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve during the second heating). The peak temperature of the melting peak in the DSC curve was determined, and this value was defined as the melting point. If multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the largest area is adopted as the melting point. In this case, the melting peak with the largest area can be determined by distinguishing each melting peak at the temperature of the trough in the DSC curve located between the peak temperatures of each melting peak and comparing the area (heat of fusion) of each melting peak. The temperature of the trough in the DSC curve corresponds to the temperature at which the value on the vertical axis of the differential curve of the DSC curve (DDSC) becomes 0, so it can also be determined from the differential curve of the DSC.

[0068] <Heat of fusion of linear low-density polyethylene and total heat of fusion of foamed particles> The heat of fusion of linear low-density polyethylene and the total heat of fusion of foamed particles used in the examples and comparative examples were measured in accordance with JIS K7122:2012. First, linear low-density polyethylene or foamed particles were used as test specimens, and the DSC curve for the second heating was obtained using the same method as described above for measuring the melting point of linear low-density polyethylene. The point on the obtained DSC curve at a temperature of 80°C was designated as α, and the point on the DSC curve corresponding to the melting end temperature was designated as β. The area enclosed by the DSC curve in the interval between points α and β and the line segment (α-β) was measured, and the heat of fusion of linear low-density polyethylene or the total heat of fusion of foamed particles was calculated from this area.

[0069] <Heat of fusion at high temperature peak of foamed particles> The heat of fusion of the high-temperature peak of the foamed particles was measured by differential scanning calorimetry in accordance with JIS K7122:2012. Specifically, approximately 2 mg of foamed particles were collected and heated from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimetry meter (EXSTAR DSC7020), and a DSC curve with two or more melting peaks (DSC curve for the first heating) was obtained. In the following description, the intrinsic peak of linear low-density polyethylene is denoted as A, and the high-temperature peak appearing at a higher temperature is denoted as B. A straight line (α-β) was drawn connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting termination temperature T of the foamed particles. The melting termination temperature T is the high-temperature endpoint of the high-temperature peak B, and is the intersection point of the high-temperature peak and the high-temperature baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which is in the valley between the intrinsic peak A and the high-temperature peak B, and the point where it intersects with the straight line (α-β) was denoted as δ. The area of ​​the region enclosed by the curve of the high-temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ) was determined, and the heat of fusion of the high-temperature peak was calculated from this area. The heat of fusion of the high-temperature peak was measured for three different test specimens, and the arithmetic mean of the obtained values ​​was taken as the heat of fusion of the high-temperature peak of the foamed particles.

[0070] <Bulk density of foamed particles> Approximately 500cm 3 The foamed particle group was filled into a graduated cylinder, and the filling height of the foamed particle group inside the cylinder was stabilized by lightly tapping the floor several times with the bottom of the graduated cylinder. The bulk volume of the foamed particle group indicated by the scale on the graduated cylinder was read and designated as V1 (L). Next, the mass of the foamed particle group was measured and designated as W1 [g]. Divide the mass W1 [g] of the foam particles by the volume V1 (W1 / V1) and convert the unit to [kg / m³]. 3 The bulk density of the foamed particles was determined by converting it to [a specific value].

[0071] <Percentage of closed cells in foamed particles> The percentage of closed cells in the foamed particles was measured as follows: Bulk volume approximately 20 cm³ 3 The apparent volume Va of the foamed particle group was measured by immersing it in ethanol. Next, after thoroughly drying the foamed particle group whose apparent volume Va was measured, the true volume Vx of the foamed particle group (the sum of the volume of the resin constituting the foamed particle and the total volume of the closed-cell portion of the foamed particle) was measured according to procedure C described in ASTM-D2856-70. A Toshiba Beckmann air-comparison hydrometer "930" was used to measure this true volume Vx. Then, the closed-cell ratio was calculated using the following formula (1), and the arithmetic mean of the results of five measurements using different foamed particle groups was obtained. Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) (1) Vx: True volume (cm³) of the foamed particle group measured by the above method 3 ) Va: The apparent volume (cm³) of the foaming particle group, measured from the rise in water level when the foaming particle group is submerged in ethanol in a graduated cylinder. 3 ) W: Mass of foaming particles (g) ρ: Density of the resin constituting the foam particles (g / cm³) 3 )

[0072] <Average bubble diameter of foamed particles> The average bubble diameter of the foamed particles was measured as follows: Thirty foam particles were randomly selected from the group of foam particles. Each foam particle was cut in half through its center, and magnified photographs of each cross-section were taken. In each cross-sectional photograph, four line segments were drawn from the outermost surface of the foam particle through the center to the outermost surface of the opposite side, such that the angles between adjacent line segments were equal. The number of bubbles intersecting each line segment was measured, and the average bubble diameter of each foam particle was calculated by dividing the total length of the four line segments by the total number of bubbles intersecting the segments. The average bubble diameter of the foam particles was then calculated by taking the arithmetic mean of these values.

[0073] <Ratio of bulk density of single-stage foamed particles to bulk density of double-stage foamed particles> The bulk density of single-stage foamed particles and double-stage foamed particles were measured using the bulk density measurement method described above. By dividing the bulk density of single-stage foamed particles by the bulk density of double-stage foamed particles, the ratio of the bulk density of single-stage foamed particles to the bulk density of double-stage foamed particles (bulk density) was calculated. 1段発泡 / bulk density 2段発泡 The ratio was calculated. Note that a larger ratio value indicates that lower bulk density two-stage foamed particles can be obtained, thus signifying superior two-stage foaming performance.

[0074] <State of two-stage foamed particles> The surface condition of the two-stage foamed particles was observed visually. A "○" rating was given when there were no clear wrinkles on the foamed particles and little shrinkage was observed, while a "×" rating was given when clear wrinkles were observed on the foamed particles and significant shrinkage was observed. Furthermore, if the above evaluation is "○", there will be little variation in density between the resulting two-stage foamed particles, making it easier to control the density of the foamed particles when manufacturing the desired molded product, and resulting in foamed particles that stably exhibit good in-moldability.

[0075] <Molding pressure range capable of producing good quality products> Using the method described later in "<Manufacturing of Foamed Particle Molded Articles>", foamed particle molded articles were formed by varying the molding pressure (molding steam pressure) in increments of 0.01 MPa between 0.10 and 0.20 MPa (G). The in-moldability of the resulting molded articles was evaluated for the following items: fusion properties, surface appearance (degree of voids), and recovery properties (recovery from expansion or contraction after in-mold molding). Articles that met the criteria shown below were deemed acceptable, and the steam pressure at which all items were accepted was defined as the steam pressure at which molding was possible. Note that pressures marked with (G) are gauge pressures, i.e., pressure values ​​relative to atmospheric pressure. A wider range from the lower limit to the upper limit of the moldable steam pressure is preferable, as it indicates a wider moldable range. (Fusibility) The foam particle molded body was bent and fractured, and the number of foam particles present on the fracture surface (C1) and the number of fractured foam particles (C2) were determined. The ratio of the number of fractured foam particles to the number of foam particles (C2 / C1 × 100) was calculated as the material fracture rate. The above measurement was performed five times using different test pieces, and the material fracture rate for each was determined. A material fracture rate of 80% or higher obtained by arithmetic mean was considered a pass, and a rate below 80% was considered a fail. (Surface appearance) A 100mm x 100mm square was drawn in the center of the foam particle molded body, and a line was drawn diagonally from one corner of the square. The number of voids (gaps) of 1mm x 1mm or larger along this line was counted. A product was deemed acceptable if the number of voids was less than 5 and the surface was smooth; otherwise, it was deemed unacceptable. (Recoverability) For a flat foam particle molded body measuring 250 mm in length, 200 mm in width, and 50 mm in thickness, obtained by in-mold molding, the thickness was measured near the four corners (10 mm inward from the corners towards the center) and at the center (the intersection of the line that bisects the molded body vertically and the line that bisects it horizontally). Next, the ratio (%) of the thickness at the center to the thickness at the thickest point near the four corners was calculated. A ratio of 95% or higher was considered a pass, and a ratio below 95% was considered a fail.

[0076] <Density of foamed particle molded body> The foamed particle molded body was left for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm. Next, its mass was measured and defined as W [g]. Next, based on the dimensions of the foamed particle molded body, the volume V [cm³] of the foamed particle molded body is calculated. 3 ] was measured. The mass W [g] of the foamed particle molded body is divided by the volume V (W / V), and the unit is [kg / m³]. 3 The density of the foamed particle molded body was determined by converting it to [a specific value].

[0077] <Compressive stress of foamed particle molded body at 50% strain> From the molded bodies obtained in the examples and comparative examples, test specimens measuring 5 cm (length) x 5 cm (width) x 2.5 cm (height) were taken, and the stress at 50% strain was measured by compressing the test specimens at a compression rate of 10 mm / min. The higher the stress, the better the strength of the foamed particle molded body. Furthermore, the obtained compressive stress at 50% strain was divided by the density to calculate the ratio of the compressive stress at 50% strain of the foamed particle molded body to the density of the foamed particle molded body. The ratio was 4 kPa / kg / m 3 ] or more than 10kPa / [kg / m 3 The following is preferable, as it represents a good balance between strength and flexibility.

[0078] <Compression set of foamed particle molded material> The compression set of the foamed particle molded article was measured in accordance with JIS K6767:1999. First, three rectangular specimens measuring 50 mm in length, 50 mm in width, and 25 mm in thickness were cut from the foam particle molded body, excluding the skin layer used during molding. Each specimen was compressed to a state of 25% strain in the thickness direction of the specimen under conditions of 23°C and 50% relative humidity, and left in this state for 22 hours. After that, the specimens were released from compression, and their thickness was measured 24 hours after the end of compression. The compression set (%) for each specimen was calculated by dividing the change in thickness of the specimen before and after the test by the thickness of the specimen before the test, and the arithmetic mean of these was taken as the compression set (%). The smaller the compression set, the better the foam particle molded body recovers its shape after compression. Therefore, foam particle molded bodies with a small compression set can be suitably used for various applications. From this viewpoint, the compression set of the foam particle molded body is preferably 3.0% or less, more preferably 2.9% or less, and even more preferably 2.8% or less.

[0079] [Linear low-density polyethylene] Table 1 shows the linear low-density polyethylene used in the examples and comparative examples. Table 1 also shows the density ρ (kg / m³) of the linear low-density polyethylene used in the examples and comparative examples. 3 We will also show whether the ) and the melting point Tm (°C) satisfy the following equation (1). ρ < 1.14 × Tm + 779 ···(1)

[0080] [Table 1]

[0081] [Manufacturing of foamed particles and molded foamed particle products] (Example 1) <Manufacturing of foamed particles> An extruder with an inner diameter of 26 mm was prepared, equipped with a die for strand formation on the outlet side. LL1 and zinc borate (arithmetic mean particle size based on number: 7 μm) as a foam regulator were supplied to the extruder and melt-kneaded to form a resin molten product. The zinc borate content in the foamed particles was supplied to 500 ppm by mass. The obtained molten resin was extruded as strands from a strand-forming die, the extruded strands were water-cooled, and then cut with a pelletizer to obtain cylindrical resin particles with an average mass of 1.5 mg per particle, a particle diameter of 1.9 mm, and a length / diameter ratio of 1.9, using linear low-density polyethylene as the base resin.

[0082] 500g of the resin particles, 3.5L of water as a dispersion medium, 3g of kaolin as a dispersant, and 0.2g of sodium dodecylbenzenesulfonate (product name: Neogen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a surfactant were placed in a 5L sealed container. Next, carbon dioxide was injected into a sealed container as a blowing agent and pressurized until the equilibrium vapor pressure shown in Table 2 was reached. Then, while stirring the contents of the sealed container, the temperature was increased to the blowing temperature (124°C) at a heating rate of 2°C / min. The temperature was then maintained at the same temperature for 15 minutes (holding step). This holding step adjusted the heat of fusion at the high temperature peak (obtained from the endothermic curve by DSC measurement). After that, the contents of the sealed container were released to atmospheric pressure to obtain blown particles (single-stage blown particles). As described above, the obtained foamed particles were left to cure for 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. Next, the cured foamed particles were filled into a pressurized sealed container, and the pressure inside the sealed container was increased from atmospheric pressure to pressurize the foamed particles. The pressurized state of the foamed particles was maintained for 24 hours to impregnate the bubbles of the foamed particles with air. After that, the foamed particles were removed from the sealed container, and foamed particles with an internal pressure of 0.5 MPa(G) were obtained. These foamed particles were then supplied to a two-stage foaming apparatus. Steam was supplied into the apparatus to cause two-stage foaming of the foamed particles, resulting in a bulk density of 22 kg / m³. 3 We obtained foamed particles (two-stage foamed particles). The foamed particles after two-stage foaming were used for the measurements described above and for the production of molded foamed particle bodies.

[0083] <Manufacturing of foamed particle molded products> After applying an internal pressure of 0.25 MPa(G) to the foamed particles with air, the foamed particles were filled into a mold capable of forming a flat plate measuring 250 mm (length) x 200 mm (width) x 50 mm (thickness), and heated using the following heating method. First, preheating (exhaust process) was performed by supplying steam to the mold with the drain valves on both sides of the mold open. Then, steam was supplied from one side of the mold to heat it, and then from the other side to heat it again. Subsequently, steam was supplied from both sides of the mold at a predetermined molding heating steam pressure to heat it (main heating). After the main heating was completed, the pressure was released, and the mold was water-cooled until the pressure on the molding surface of the mold reached 0.04 MPa (G), at which point the mold was opened and the foam particle molded body was removed. The resulting molded body was cured in an 80°C oven for 12 hours to obtain a foamed particle molded body (polyethylene-based resin foamed particle molded body). In the evaluation of the aforementioned <molding pressure range capable of producing good products>, molding was performed by changing the molding pressure. Table 2 shows the measurement results of the physical properties of the obtained foamed particles and the evaluation results of the molded products. The biomass content of the foamed particles, the density of the resin constituting the foamed particles, and the melting point of the foamed particles were the same as those of the linear low-density polyethylene used to produce each foamed particle. Furthermore, each foamed particle was uncrosslinked.

[0084] (Examples 2-7) In Example 1, foamed particles and polyethylene-based resin foamed particle molded articles were obtained in the same manner as in Example 1, except that the linear low-density polyethylene, foaming temperature, and equilibrium vapor pressure were changed to the conditions shown in Table 2. The measurement results of the physical properties of the obtained foamed particles and the evaluation results of the molded articles are shown in Table 2.

[0085] (Comparative Examples 1-7) In Example 1, foamed particles and polyethylene-based resin foamed particle molded articles were obtained in the same manner as in Example 1, except that the linear low-density polyethylene and foaming temperature were changed to the conditions shown in Table 3. The measurement results of the physical properties of the obtained foamed particles and the evaluation results of the molded articles are shown in Table 3.

[0086] [Table 2]

[0087] [Table 3]

[0088] The results shown in Table 2 indicate that the foamed particles of the examples can be used to produce foamed particle molded articles over a wide density range and exhibit excellent in-moldability. Furthermore, the resin particles related to the foamed particles of the examples exhibit excellent foamability. Moreover, the polyethylene-based resin foamed particle molded articles produced using the foamed particles of the examples exhibit low compression set. Therefore, the polyethylene-based resin foamed particles of the present invention exhibit excellent in-moldability, and the polyethylene-based resin foamed particle molded articles obtained using these foamed particles have low compression set and can be suitably used for various applications.

Claims

1. Foamed particles using linear low-density polyethylene as the base resin, The density of the aforementioned linear low-density polyethylene is 920 kg / m³. ３ The following: The melting point of the linear low-density polyethylene is 120°C or higher and 130°C or lower. The linear low-density polyethylene comprises, as copolymerization components, a propylene component and one or more α-olefin components (α1) selected from butene components, hexene components and octene components. Foamed particles in the linear low-density polyethylene, wherein the sum of the content of the propylene component and the content of the α-olefin component (α1) is 1 mol% or more and 10 mol or less, and the ratio of the content of the propylene component to the sum of the content of the propylene component and the content of the α-olefin component (α1) is 0.1 or more and 0.6 or less.

2. The foamed particle according to claim 1, wherein the content of the propylene component in the linear low-density polyethylene is 0.5 mol% or more and 3 mol% or less.

3. The foamed particle according to claim 1 or 2, wherein the density ρ (kg / m³) of the linear low-density polyethylene and the melting point Tm (°C) of the linear low-density polyethylene satisfy the following formula (1): ρ < 1.14 × Tm + 779 ... (1)

4. The foamed particle according to claim 1 or 2, wherein the biomass content of the linear low-density polyethylene, as measured by ASTM D 6866, is 40% or more.

5. The foamed particles have a crystalline structure in which, in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, a melting peak (intrinsic peak) characteristic of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear on the high-temperature side of the intrinsic peak. The total heat of fusion of the foamed particles is 70 J / g or more and 100 J / g or less. The heat of fusion of the aforementioned high-temperature peak is 10 J / g or more and 50 J / g or less. The foamed particles according to claim 1 or 2.

6. The foamed particle according to claim 5, wherein the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the foamed particle is 0.2 or more and 0.7 or less.

7. The bulk density of the foamed particles is 10 kg / m³ 3 More than 300kg / m 3 The foamed particles according to claim 1 or 2, which are as follows:

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